1. Field of the Invention
The present invention relates to a monolithic nozzle assembly for fluid formed using a mono-crystalline silicon wafer, and a method for manufacturing the same by continuous self-alignment.
2. Description of the Related Art
A laminated ink jet recording head disclosed in EP 0 659 562 A2 is shown in FIG. 1A. As shown in FIG. 1A, the laminated ink jet recording head has a nozzle plate 101 with a nozzle 100, three plates 201a, 201b and 201c with communication holes, a plate 301 with a pressure producing chamber 300, and a vibration plate 400, which are stacked in sequence. Ink contained in an ink tank 800 flows through an inlet 700 into a reservoir chamber 600a, and is temporarily stored in the reservoir chamber 600a. As the ink flows through an ink inlet 600c and the communication hole 600b into the pressure producing chamber 300, the ink tank 800 fills with ink. A filter 900 for filtering the ink supplied from the outside is located on the top of the ink tank 800. The vibration plate 400 has piezoelectric vibration elements, so that a predetermined pressure can be applied to the ink filling the pressure producing chamber 300 according to a voltage signal applied to the piezoelectric vibration elements. As a result, ink is discharged out of the nozzle 100 through the communication holes 200a, 200b and 200c. The laminated ink jet recording head having the configuration needs align and bonding processes to combine each of the plates. As illustrated in FIG. 1B. a complicated assembling process is needed to combine each plate, which lowers yield and efficiency. Furthermore, an alignment error occurs during the alignment. In particular, the nozzle assembly indicated by xe2x80x9cAxe2x80x9d in FIG. 1A, including a damper serving as a flow path of fluid and nozzle, are formed by depositing the plates having different sized holes. The conventional nozzle assembly nozzle assembly, which effects a smooth fluid flow and discharge of ink droplets, is formed by depositing the individual plates. Thus, if the individual plates are misaligned, a directional smooth flow of fluid is not obtained.
The nozzle assembly can be manufactured in a variety of ways, as illustrated in FIGS. 2A through 2F, FIGS. 3 and 4, and FIGS. 5A through 5C. The illustrations of the drawings are limited to the formation of nozzles. Thus, additional deposition processes are needed to form a damper. These additional deposition processes are disadvantageous in terms of efficiency and yield, as described above.
In particular, FIGS. 2A through 2F illustrate a method for forming nozzles, which is disclosed in U.S. Patent No. 3,921,916. Referring to FIGS. 2A through 2C, a selective doping is performed on one surface of a substrate. Then, the opposite surface of the substrate is wet etched, as shown in FIG. 2D. During the wet etching, only the doped silicon is selectively etched, forming a nozzle part, as illustrated in FIGS. 2E and 2F. Limitation of this method are related to doping depth and overall processing complexity.
FIG. 3 illustrates a method for forming nozzles by mechanical punching. This method results in uneven cut surfaces and a low yield. In addition, the method is applicable only to the structure formed by deposition.
FIG. 4 illustrates a method of forming nozzles, which was described in an article by Jafar Haji Babaei, et al., entitled xe2x80x9cAn integrable nozzle for monolithic microfluid devices,xe2x80x9d published in Sensors and Actuators A, Vol. 65 (998), pp. 221-227. According to this method, the nozzle is formed by a two-side alignment and a time-controlled wet etching. The nozzle size is determined depending on the depth of etching and the feature size of a mask pattern used for wet etching. Thus, there is a problem of uniformity. It is inconvenient to stop the etching process by measuring time.
FIGS. 5A through 5C illustrate a method for forming nozzles, which was described in an article by G. Siewell, et al., entitled xe2x80x9cThe thinkjet orifice plate: A part with many functions,xe2x80x9d published in the Hewlett-Packard Journal, Vol. 36, No. 5, (May 1985), pp. 33-37. In particular, a photoresist pattern is applied on a portion of the substrate, as illustrated in FIG. 5A. Then, nickel (Ni) is deposited on the structure exclusive of a pattern deposited portion to be nozzles by electroplating, as illustrated in FIG. 5B. Then, the Ni plated layer is separated from the substrate, as illustrated in FIG. 5C, thereby completing a nozzle part. The size of nozzles formed through this method varies in the range of a few microns, and the tilt angle of the nozzle part cannot be accurately adjusted.
FIGS. 6A and 6B, and FIGS. 7A through 7D illustrate conventional methods for manufacturing a nozzle assembly by combining two silicon wafers each having a damper and nozzle part made of silicon. Referring to FIGS. 6A and 6D, a bulk silicon wafer 20 having a damper 21 is attached to a nozzle plate 30 having a nozzle opening 31 to form a nozzle assembly. In another method, referring to FIG. 7A, first a damper 42 is formed in a bulk silicon wafer 40. Then as illustrated in FIG. 7B, a wet etch mask 42 is deposited on the sidewalls of the damper 41, and a nozzle plate 50 is prepared. The bulk silicon wafer 40 is stacked on the nozzle plate 50, as illustrated in FIG. 7C. Then, as shown in FIG. 7D, the portion of the nozzle plate 50, which is exposed through the damper 41, is wet etched to form a nozzle opening 51.
For both of the methods described above, a thin wafer is used as the nozzle plates 30 and 50, so that careful handling is required to keep the thin nozzle plates 30 and 50 from breaking. The method illustrated in FIGS. 6A and 6B needs a damper-to-nozzle alignment in combining the bulk silicon wafer 20 and the nozzle plate 30. Although the method described with reference to FIGS. 7A through 7D requires no alignment, there is a problem of handing two separated fragile wafers.
FIGS. 8A through 8C illustrate a nozzle structure formed using the characteristic of the crystal planes of silicon by wet etching. In particular, FIG. 8A illustrates the crystal planes of silicon. The etch rate of the (111) silicon plane in an etchant such as trimethylammonium hydroxide (TMAH) is slower than the (100) silicon plane. As a result, the (100) silicon plane is etched, as shown in FIGS. 8B and 8C.
FIG. 9 illustrates the formation of a nozzle structure by dry etching. As illustrated in FIG. 9, because the thickness of a coated layer is not uniform over the structure, i.e., because the coated layer is thicker at the trench sidewall portion c than at the portion a, uniform dry etching with plasma is difficult.
In the nozzle assembly having a damper outlet and a nozzle, the nozzle guide controls the flow of a fluid for smooth discharge. Additionally, the nozzle serves as the outlet of a valve, or a deposition unit, such as printer heads. The damper outlet enables fluid to flow in a direction, and serves as an auxiliary discharging unit as well as a damper.
A conventional method for forming a stepped nozzle assembly having a nozzle and a damper outlet with a silicon wafer by a micro-electro mechanical system (MEMS), wherein a single step of the stepped structure has a height greater than tens of microns, is illustrated in FIGS. 10A through 10K. In particular, FIGS. 10A and 10B are sectional views of substrates for nozzle assemblies each having multiple steps. FIGS. 10C and 10D are sectional views illustrating problems in the manufacture of a nozzle assembly with such a multi-step configuration. For example, reference numeral 5 indicates a void 5 formed in a deep trench during deposition of a photoresist layer. FIGS. 10E through 10K are sectional views illustrating a method for manufacturing the nozzle assembly shown in FIG. 10A with multiple stepped masks.
For the nozzle assembly illustrated in FIG. 10A, a bulk silicon wafer 80 is prepared first, as shown in FIG. 10E. Following this, as shown in FIG. 10F, a first mask 60 is deposited on the bulk silicon wafer 80. As shown in FIG. 10G, a second mask 70 is deposited over the entire surface of the bulk silicon wafer 80. As shown in FIG. 10H, an aperture 71a for use in forming a damper is formed in the second mask 70. Then, as shown in FIG. 10I, the portion of the bulk silicon wafer 80 which is exposed through the aperture 71a is etched to form a damper 75. Then, as shown in FIG. 10J, the second mask 70 deposited on the top of the bulk silicon wafer 80 is removed. Then, the exposed portion of the bulk silicon wafer 80 is etched, resulting in a stepped configuration, as shown in FIG. 10K.
In the manufacture of a nozzle assembly having such a stepped configuration, it is difficult to uniformly deposit photoresist on a wafer. When a photoresist is deposited by spin coating, obtaining a uniform deposition of the photoresist is difficult due to centrifugal force. In addition, a void 5 is formed in a deep trench during deposition of photoresist, as shown in FIG. 10D. This void 5 causes breakage of the coated photoresist layer during a baking process. These problems occurring in the deposition of photoresist can be solved with multiple stepped masks, as described with reference to FIGS. 10E through 10K.
However, the method performed with such multiple stepped masks cannot be applied to form a conical nozzle as shown in FIG. 10B, because the first and second patterns need to be protected during etching into the third pattern, and the third pattern needs to be protected during etching into the first or second pattern. For this reason, the process performed with multiple stepped masks, which is described with reference to FIGS. 10E through 10K, cannot be applied to form a conical nozzle.
When a nozzle is formed as an outlet for fluid, there is.a need to perform hydrophilic or hydrophobic surface treatment around the nozzle. Conventional methods, such as those described above, render determination of the hydrophilic-and-hydrophobic boundary virtually impossible.
It is an object of the present invention to provide a monolithic nozzle assembly with a simple configuration, and a method for manufacturing the same, in which a nozzle assembly can be fully integrated in a single mono-crystalline silicon wafer by semiconductor manufacturing processes and MEMS process at a low cost.
According to an aspect of the present invention, there is provided a monolithic nozzle assembly formed with a mono-crystalline silicon substrate, comprising: a damper for temporarily storing an incoming fluid; and a nozzle having a pyramidal portion and an outlet portion, the pyramidal portion for guiding the flow of the fluid from the damper toward the outlet portion and for increasing the pressure of the fluid, and the outlet portion through which the fluid is discharged, wherein the damper, and the pyramidal and outlet portions of the nozzle are aligned with each other and formed in the single mono-crystalline silicon substrate by continuous processes.
It is preferable that the monolithic nozzle assembly further comprises a flow path through which the fluid is supplied into the damper, and a channel for connecting the flow path and the damper. Preferably, the mono-crystalline silicon substrate is the (100) mono-crystalline silicon substrate.
According to another aspect of the present invention, there is provided a method for manufacturing a monolithic nozzle assembly with a mono-crystalline silicon substrate by continuous self-alignment, the monolithic nozzle assembly including a damper for temporarily storing an incoming fluid, and a nozzle having a pyramidal portion and an outlet portion, the pyramidal portion for guiding the flow of the fluid from the damper toward the outlet portion and for increasing the pressure of the fluid, and the outlet portion through which the fluid is discharged outside, the method comprising: (a) depositing a first mask over the entire surface of a (100) mono-crystalline silicon substrate; (b) forming a first aperture in a portion of the first mask to be the damper and the nozzle by photolithography; (c) etching a portion of the substrate which is exposed through the first aperture to form the damper; (d) depositing a second mask along the inner wall of the damper, the second mask for protecting the damper from a subsequent wet etching process; (e) removing the second mask from the bottom of the damper by anisotropic dry etching to form a second aperture for use in forming the nozzle; (f) forming the pyramidal portion of the nozzle in the (100) mono-crystalline silicon wafer by wet etching; (g) forming a third aperture in the first mask deposited on the backside of the silicon wafer, the third aperture for use in forming the output portion of the nozzle; (h) forming the outlet portion of the nozzle using the third aperture; and (i) removing the first and second masks.
It is preferable that the first aperture in step (b), and the second aperture in step (g) are formed by photolithography. The first mask in step (a) is preferably formed of an oxide layer, nitride layer, or a metal layer. Preferably, the first aperture formed in step (b) has a circular cross-section. Preferably, forming the damper in step (d) is performed by anisotropic dry etching with an inductively coupled plasma reactive ion etching (ICP RIE), plasma-tourch, or laser punching apparatus. It is preferable that a wafer having an etch stopper is used as the (100) mono-crystalline silicon substrate. It is preferable that the second mask in step (d) is formed of the same material as the first mask formed in step (a) with a larger thickness difference with respect to the first mask, or is formed of a different material from the first mask with a high etch selectivity with respect to the first mask for the anisotropic dry etching of step (e). Alternatively, the first mask may be formed of a nitride layer, and the second mask may be formed of an oxide layer. It is preferable that, in step (f), the pyramidal portion of the nozzle is formed using the anisotropic wet etching characteristics of the (100) and (111) crystal planes of silicon substrate.